A rubber belt or a chain is used for driving a camshaft of an internal combustion engine of an automobile, driving an auxiliary unit such as an injection pump, or transmitting power in an industrial machine. Generally, a rubber belt includes a rubber portion and a reinforcing cord embedded in the rubber portion. Since the strength of the rubber belt depends on the strength of the reinforcing cord, the reinforcing cord is an important component that determines the life of the rubber belt. Such reinforcing cords are conventionally proposed (see, for example, Patent Literature 1).
Glass fibers have mainly been used as reinforcing fibers for use in cords for reinforcing rubber products. However, with recent developments in science and technology, the cases where glass fibers cannot adequately meet the performance requirements for reinforcing fibers have been increasingly reported. Therefore, as alternatives to glass fibers, various types of reinforcing fibers such as aramid fibers, polyparaphenylene benzobisoxazole fibers, and carbon fibers have been studied. Among these types of fibers, carbon fibers are particularly preferred as reinforcing fibers due to their advantages of high strength and high elastic modulus.